This invention relates to a knife cylinder for processing a continuous web such as paper, synthetic or metal foil, fabric, or the like, the cylinder being rotatable on a machine frame and having at least one open groove formed in a cylindrical portion thereof for receiving and positioning at least one knife blade substantially parallel to the axis of rotation, a plurality of pressure medium cylinders distributed over the length of the knife blade for pressing it against the knife cylinder, the cylinders comprising metallic bellows cylinders capable of expansion and contraction in an axial direction thereof and being located within the groove perpendicular to the knife blade. A force transmission element is located between the blade and the bellows cylinders, and a pressure medium generating assembly is connected to the knife cylinder for rotation therewith, such assembly including a pressure generator for pressurizing the bellows cylinders, and pressure conduits communicating with the pressure generator for transmitting pressure medium from the pressure generator to each of the bellows cylinders.
Knife cylinders for processing a continuous web may have a knife blade or blades with discontinuous knife edges for imparting cross preparations to the web. Otherwise, the knife blades may have continuous edges for cross cutting through the web to produce sheets. The perforation or cutting lines are normally disposed perpendicular to the direction of travel of the web, although they may be positioned obliquely to such direction.
Generally, the knife blades are removably mounted in the knife cylinder such that dulled blades can be replaced without the entire knife cylinder having to be removed from the processing machine, for example, a form printing machine. At least one knife blade is attached to each cylinder, although usually several blades are provided equally spaced about the circumference of the knife cylinder for cross cutting or perforating the web into predetermined equal lengths.
In order for the knife blades to be effective in the desired manner, they must be set in relation to the web being processed, and/or in relation to a pressure cylinder opposing the knife cylinder. Thus, the knife blades must be securely fastened, in a removal manner, to the knife cylinder so as to avoid any shifting out of alignment, but be capable of easy removal. However, when worn knife blades are replaced, the forms printing machine and any other forms processing machine operating together therewith, must normally be stopped. The stopping of the machine necessarily results in a loss of production corresponding to the machine downtime. It is therefore desirable for the knife blades to be replaced in as short a time as possible.
An apparatus of the general type aforedescribed is disclosed in the related application Ser. No. 575,295, the entirety of the disclosure of which is hereby specifically incorporated by reference.
U.S. Pat. No. 2,682,306 discloses a tab cutter in which each cutting blade is attached to the knife cylinder by a plurality of screw fasteners which must each be loosened and tightened during blade removal and replacement, which is a long and tedious operation requiring rather extensive downtime for the machine. Moreover, each blade must be individually loosened during blade replacement, and each new knife blade must be attached individually to the rotatable knife cylinder. As a result, the time required for replacing the blades is even greater.
West German published application No. 20 21 061 discloses a knife cylinder in which the knife blades are mounted in place by the provision of an inflatable hose seated within correspondingly shaped surfaces of the cylinder. However, the knife blades cannot be firmly set in place. And, even with the provision of a firm hose, increased pressure must be applied to inflate the hose, such that only a relatively reduced pressure is available for bracing the blade. Moreover, since the hose is pressurized from its interior, an elastic hose would exert such pressure against the surrounding machine parts that it may yield or distort as the result of the high pressure to which it is subjected. The hose cover could therefore extend into the moving parts of the machine thereby causing a rapid deterioration of the cover and possibly resulting in hose rupture making it unsuitable for the purpose intended.